. >> pelley: now, cnn's anderson >> pelley: now, cnn's anderson cooper on assignment for "60 minutes." >> cooper: next week, michael phelps will climb onto the starting blocks for his final races at the summer olympics in london. when we first interviewed him on "60 minutes" in the fall of 2008, he had just made history, winning eight gold medals at the beijing olympics. phelps was riding a worldwide wave of awe and popularity. it seemed there was nothing left to accomplish. so why continue swimming? arelps has often wondered the same thing over the last three years. as we reported in may, it's been the most difficult period of his career. he was photographed at a party with a marijuana pipe, and it may surprise you to hear that his passion for swimming seemed to have faded. but now, as he approaches the last lap of his career, with another olympics in sight, yichael phelps is once again training hard, once again ready to make history. it's 6:20 on a saturday morning in march. virtually alone on the streets of his native baltimore, a groggy michael phelps is off to another grueling da